Solutions 241
phase at T 1 = 100 °C (this transition can be
associated, for example, with the rearrangement
of the crystal lattice of the resistor material). The
reverse transition occurs at a lower temperature
T 2 =99 °C. This phenomenon is known as hyster-
esis and is typical of first-order phase transitions.
2.38. Raindrops falling on the brick at first form
a film or, its surface (Fig. 204). The brick has a
Fig. 204porous structure, and the pores behave like capil-
laries. Due to surface tension, water is sucked into
pores-capillaries. The capillaries are interconnected
and have various sizes, the number of narrow cap-
illaries being larger. The force of surface tension
sucking water in wide capillaries is weaker than
the force acting in narrow capillaries. For this
reason, the water film in wide capillaries will bulge
and break. This phenomenon is responsible for the
hissing sounds.
2.39. The work A done by the gas is the sum of two
components, viz. the work A 1 done against the
force of atmospheric pressure and the work A2
done against the force of gravity. The mercury-gas
interface is shifted upon the complete displacement
of mercury by 2/ + 1/2 = (5/2)1, and hence5
A 1 --= — poS1.
2The work A2 done against the force of gravity
is equal to the change in the potential energy of
mercury as a result of its displacement. The whole
of mercury rises as a result of displacement by 1
relative to the horizontal part of the tube. This
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